The polyanion based materials gained significant interest since the discovery of LiFePO₄ as a safer cathode material in 1997 [1], and of Li₂FeSiO₄as a new Li-battery cathode material in 2005 [2]. Lithium transition metal orthosilicates are promising cathode candidates since they allow Li extraction/insertion beyond one Li-ion per formula unit. Additionally, they consist of cheap, environmentally benign and abundant elements [3]. However, these materials suffer from poor conductivity, ionic as well as electronic, which demands the need for nanostructuring and conductive coatings. And in order for the orthosilicates to be real competitors to current commercial cathode technology, it is vital to find cost efficient and scalable methods for production of nanosized powders.

Here, we present a time-efficient and scalable aerosol combustion method with subsequent annealing, leading to nanoscale and carbon-coated Li₂FeSiO₄ and Li₂Fe_0.5Mn_0.5SiO₄. Using liquid-feed flame spray pyrolysis, we demonstrate synthesis of highly phase pure materials in a relatively short time. The work shows the importance of synthesis parameters such as precursor concentration, and its effect on particle size, degree of agglomeration, and long-term performance. In the case of Li₂FeSiO₄, the optimised precursor concentration yielded particles of about 30 nm, which delivered an initial discharge capacity of up to 150 mAhg^-1 at 60 °C and C/20. Furthermore, over 50% of the capacity is retained at a high rate of 5C, and long-term cycling showed outstanding capacity retention of over 90% after 300 cycles at a moderate rate of C/2. Li₂Fe_0.5Mn_0.5SiO₄ on the other hand_,was shown to suffer from a severe capacity fade, and upon prolonged cycling the redox activity can be attributed solely to Fe.

[1]    Padhi A. K., Nanjundaswamy K. S., Goodenough J. B., J. Electrochem. Soc, 1997, 144, 1188-1194.

[2]    Nyten A., Abouimrane A., Armand M., Gustafsson T., Thomas J. O., Electrochemistry Communications, 2005, 7, 156-160.

[3]    Saiful Islam M., Dominko R., Masquelier C., Sirisopanaporn C., Armstrong A. R., Bruce P. G., J. Mater. Chem., 2011, 21, 9811-9818